Physico-Chemical Effects on the Scale-Up of Ag Photodeposition on TiO2 Nanoparticles

We have previously demonstrated that TiO₂ nanoparticles can be functionalized by photodeposition with silver or gold particles in the 1?C2 nm range presumed to be desirable for catalysis applications. However, the preparation of these samples directly on microscope grids, while conducive to particle size determinations, did not produce sufficient materials for reaction studies. We report here scale-up techniques designed to produce greater quantities of material for testing, while maintaining characteristics that contribute to uniformity in the deposition process. For the scale-up process, an irradiation source with highly uniform intensity is necessary to generate Ag/TiO₂ samples with consistent Ag loading. In addition, control of the precursor concentration is also required to produce Ag/TiO₂ samples with high Ag loading and narrow Ag size distribution. The optimum conditions for the scale-up process found in this study involved Ag photodeposition from a 5 × 10^?3 M AgNO₃ solution using a high pressure Hg lamp at 366 nm for 60 s. Under these reaction conditions, the size of Ag particles determined by TEM and HAADF-STEM imaging was within 1?C2 nm and the Ag loading was ~3.2 wt%. Achievement of this level of uniformity required control of the uniformity of illumination, as well as of the solution concentration and irradiation conditions. Higher solution concentrations and higher power led to the growth of larger (ca. 10 nm) silver particles. In contrast, the loading and size distribution of the Ag particles photodeposited were remarkably insensitive to the source and morphology of the TiO₂ nanoparticles utilized. No Ag peak was resolved in the XRD patterns for Ag/TiO₂ samples obtained from the optimized scale-up process, corroborating the size range determination of the Ag nanoparticles. XPS showed that the Ag particles in all cases were metallic Ag.